When open-celled polyisocyanate-based polymers such as flexible polyurethane foams are prepared, it is important to ensure that the foam has a sufficient quantity of open cells to prevent shrinkage on curing. The preparation of flexible polyurethane foam is nearly always accompanied by the formation of some closed cells. The presence of closed cells substantially reduces the dimensional stability and flexibility of the foam while increasing its rigidity and brittleness. The closed cell content of a foam can be reduced by mechanical means such as crushing or flexing of the foam during its curing process causing the closed cells to be ruptured and opened. Alternatively, the extent of formation of closed cells can be minimized in part by careful selection of surfactants and/or stabilizers and particular choice of urethane catalysts and their levels for the preparation of the foams. For example, U.S. Pat. Nos. 3,748,288 and 3,884,848 teach the use of surfactants which are hydrophobic organosilicones for improving the open cell content of a foam. In U.S. Pat. No. 4,596,665, the use of polyoxybutylene alcohols as a cell opening agent is taught in the preparation of lower resilience polyurethane foams.
Other additives such as polyolefins, waxy hydrocarbons such as paraffin oil, are commonly employed as cell opening agents. However, they suffer from problems in incompatibility with the reactants and the foam itself.
A common problem with nearly all conventional cell openers is that they cause deterioration in the mechanical properties of the foams, especially compressive strengths. Since they do not contribute to the overall properties of the foam, except to open cells, it is desirable to reduce the quantity of cell opener required or modify it in such a way that it may contribute to the properties of the foam. For example, U.S. Pat. No. 4,493,909 teaches the use of poly-N,N-hydroxyalkylamides of polybasic carboxylic acids in the production of highly elastic polyurethane foams as a cell opening agent. The efficiency of these products as cell opening agents is dependent on a primary hydroxyl content and, in addition, is largely dependent on the nature of the carboxylic acid used in its preparation.
Accordingly, it would be desirable to provide a cell opening agent which can assist in cell opening and maintain the mechanical properties of the foam and one in which the properties are not dependent on the presence of primary hydroxyl groups.